He told Tonight With Trevor McDonald: "What we see is kids watching these shows and thinking, 'well maybe I could stage my own scenes of pain and humiliation along these lines'."

He said it is seen by the "slappers" as a shortcut to "fame and notoriety among the people who see the images circulated on the web or sent to them via their mobile phones".

An MTV spokesman stressed that the shows referred to were aired at "appropriate" times with several warnings and that viewers were told submissions would not be looked at.

But youngsters who claim to know about happy slapping culture seem to agree with Dr Barnfield.

Manny Logan, 16, from south London, told the Tonight with Trevor McDonald
special, Mugging for Kicks: "You see someone just sitting there, they look like
they're dumb. You just run up to them and slap them. And run off. It's funny."

Armand Jenkins, 16, said: "Even though it might be quite painful for them and you obviously feel quite sorry for them because they're injured... it's still funny because it's like seeing the sketch on TV."

But not everyone is laughing.

Mr Prescott says he was intimidated by youths clad in hooded tops

Paul Fawcett, a spokesman for Victim Support, said he knew of a colleague who had been attacked in the way described.

He said: "Being assaulted under any circumstances, whether verbally or violently, is very upsetting.

"People affected by such crime heal more slowly than those who have suffered from an accident because they know that somebody decided to hurt them on purpose."

Mr Fawcett said the use of mobile phones to film an attack added a new dimension because it meant there was "no other reason for the assault, such as money or drugs, other than the gratification of inflicting pain".

News of the trend has prompted widespread fear of groups of young people clad in hooded tops.

Bluewater shopping centre in Kent has banned hooded tops, baseball caps and swearing as part of a zero-tolerance crackdown on intimidating behaviour.

And Deputy Prime Minister John Prescott has backed the move, claiming hoods are part of an "intimidating" uniform after he was confronted by youths at a motorway cafe.

Real threat?

But is happy slapping a genuine trend or media hype?

Victim Support are unsure.

"This behaviour seems to be too new to say how widespread it is or the extent to which it exists," said Mr Fawcett.

A Police Federation spokeswoman said: "Obviously this kind of behaviour is illegal.

"At the very least this could be classed as a common assault."

A conviction for assault could lead to up to five years in jail.

The spokeswoman said it was difficult to establish a national picture of how widespread the behaviour has become because cases are handled by individual forces.